Lung cancer represents the most frequent neoplasm in American males. Small cell carcinoma of the lung, a highly lethal cell type, has recently been described as having a consistent deletion of the short arm of chromosome 3(p14-23). Identification of the genetic material consistently lost may lead to greater understanding of the pathogenesis of small cell carcinoma of the lung and may perhaps aid in the development of rational schemes for treatment and prevention. This research focuses on identification of cell surface antigens expressed in rodent human somatic cell hybrids using monoclonal antibody techniques to investigate the following questions. (1)\What cell surface antigens are encoded by chromosome 3? (2)\What cell surface antigens are expressed by the deleted segment of chromosome 3 lost in small cell carcinoma? (3)\What cell surface antigens are expressed by small cell carcinoma? (4)\What cell surface antigens are expressed by normal cells, but not by small cell carcinoma? and (5)\Are any cell surface antigens unique to small cell carcinoma? During the first year of this project, somatic cell hybrids between rodent cells and human small cell carcinoma lines that appear to have retained the abnormal chromosome 3 have been produced. In addition, two monoclonal antibodies which recognize chromosome 3-encoded cell surface antigens have been identified. Preliminary mapping studies localize the genes for these antigens to the long arm of chromosome 3. By understanding the genetic abnormality in this common malignancy, we hope to gain greater insight into its initiation, pathogenesis, diagnosis, and treatment. (K)